Many optoelectronic devices consist of a quantum structure or quantum region embedded within a semiconductor heterostructure. These quantum regions may take the form of a quantum well, a superlattice, a quantum wire or a quantum dot. When manufacturing such semiconductor optoelectronic devices it is extremely important to control the optical band gap of the quantum structure. The monolithic integration of optoelectronic components requires the production of a heterostructure which has different transition energy levels across different areas of its surface. Achieving these different transition energy levels is known as “band gap tuning”.
One known method of band gap tuning a semiconductor heterostructure is known as “impurity induced quantum well intermixing”. This technique employs the diffusion of impurity atoms to enhance the quantum well intermixing. An example of this technique is described in U.S. Pat. No. 5,815,522 (Nagai).
This technique has the disadvantage that the diffusion of the impurities may alter the electrical properties of the semiconductor and deteriorate the optical quality of the device. For this reason, impurity induced intermixing is not quite suitable for the fabrication of active devices.
Another known method is called “ion-implantation induced intermixing.” According to this technique, the intermixing is enhanced by the defects generated during ion implantation. Alternatively, the intermixing may be enhanced by ions implanted directly into the active region of the semiconductor. An example of this technique is described in U.S. Pat. No. 6,027,989 (Poole et al).
One application of the technique is described in U.S. Pat. No. 6,005,881 (Ikoma). That patent discloses a method of generating a semiconductor laser using ion implantation induced quantum well intermixing. The laser produced by that technique has a transparent output window structure which is suitable for high-powered operation.
However, one disadvantage of this method is that the ion implantation causes damage to the semiconductor heterostructure.
Another known method is called “impurity free vacancy enhanced disordering” (IFVD). According to this technique, a dielectric layer is deposited on top of the heterostructure in order to generate atomic vacancies at the interface of the dielectric layer and the semiconductor surface. These vacancies are generated at an elevated temperature. According to this technique the generated vacancies then diffuse into the heterostructure and thereby enhance the interdiffusion of atoms across the heterostructure.
The present inventors have developed a method for forming a modified semiconductor having a plurality of band gaps which overcomes or ameliorates at least some of the disadvantages of the prior art.